In the long run, diesel fleets will be replaced with ones powered by electricity generated using natural gas turbines, says Chris Combs, vice president for Evolution Well Services.
“There are several advantages to powering a fleet with natural gas-generated electricity, including fuel savings,” he says. “Assuming a cost of $1.85 an Mcf, which is on the high side for field gas, and assuming 25,000 downhole horsepower, powering our 48,000-horsepower fleet would cost only $300-$350 an hour. With diesel at $2.75 a gallon, fueling a traditional fleet would cost $6,000-$7,000 an hour.”
In most applications, Combs estimates that switching to natural gas reduces fuel costs by 95 percent. He adds that the turbine runs on field gas with widely varying quality. “In the field, the turbine has consumed gas with Btu content between 700 and 1,450. The richer the gas, the less it consumes and vice versa,” he says.
Reliability contributes to electric fleets’ strong economics, Combs adds. “Because there are fewer mechanical failure points, electric motors are easy to maintain. Our standard maintenance protocol for the AC motors is to grease the bearings every 12 hours, and they essentially will last forever.”
The simple maintenance and reliability have paid off, Combs says. “Our first commercial fleet runs an average of 16 hours a day in an area where conventional fleets can manage only 7-8 hours before unplanned downtime becomes cost-prohibitive. The longer run times have enabled the operator to switch from stack fracs to zipper fracs, which are more efficient,” he relates.
Because Evolution Well Services uses a single natural gas-powered turbine to generate electricity at a well site, the pump trailers no longer need diesel engines and transmissions. The company says this frees enough space for each trailer to include two pumps, meaning the fleet provides high horsepower in a small footprint.
The turbine that powers Evolution’s fleet also powers Boeing 747s and the Airbus 300 series, Combs reports. “It is extremely reliable,” he says. “Between startup and the first turbine hot section overhaul, it can run 25,000-30,000 hours, or about eight years in a hydraulic fracturing application. There is a fair chance the pumps, blenders and other process equipment will be exhausted fully before we perform the first turbine overhaul.”
Because it burns natural gas, Combs continues, the turbine’s emissions are well below the Environmental Protection Agency’s Tier 4 Final standard, which modern engines must meet. “Noise levels are much lower as well,” he adds. “At a distance of one meter from the turbine, they measure about 82 decibels, well below the Occupational Safety and Health Administration’s threshold for ear plugs.”
At that level, personnel on location can talk without raising their voices, Combs says. He describes the fleet as a great fit for operators who need to work in close proximity to homes, businesses and public spaces.
“In areas where space is limited, such as the Northeast and Rocky Mountains, the electric fleets have another advantage: a small footprint,” Combs says. “Because all the pumps are powered by a single turbine, it is no longer necessary to put an engine and transmission on each trailer. With the extra space, we replace the 2,250- or 2,500-horsepower pump that normally would be on each trailer with two, 3,000-horsepower pumps.”
The higher horsepower concentrations reduce the number of trailers on location and the spread’s overall footprint by 55-60 percent, Combs calculates. He adds that each fleet only requires a crew of 11.
“For safety and efficiency, all equipment is operated from the data van,” Combs says. “There is rarely a reason for the crew to step outside. With the exception of the master bleed off valves, which are manual for safety reasons, all the valves are remotely actuated. The van’s dual-level design provides a ‘crow’s nest’ view of the location. That is augmented by high-resolution cameras on top of the van, each pump, the blender tub, the hopper, and the hydration unit, so the crew can see everything it needs to from the van.”
In 2017, Combs reports that Evolution had a total recordable incident rate of 0.0 with a single fleet commercialized the entire year. He says that fleet worked in the Permian Basin, the Eagle Ford, and the Marcellus and Utica on demonstrations and attracted enough interest that the company is building five more this year. These fleets are committed to major U.S. onshore producers on multiyear contracts, so Evolution is expanding more.
“In the next few years, when the fracturing industry needs to build or replace horsepower, service providers will want it to be electric. In fact, we see significant evidence other service providers are looking at developing electric fleets,” Combs says. “With the right technology, it already is possible to build turbine-powered equipment at a price-per-horsepower comparable to a diesel fleet, and the price only will go down over time. Given the economic, environmental and safety benefits electric fleets offer, that is great news.”